Counterbalance valves are used to hold hydraulic fluid in hydraulic cylinders so that pistons within the cylinders retain their position without drifting. Counterbalance valves may be made in various sizes and ratios, with various numbers of ports, and can be configured as single or double valves. They are necessary when used with four-way controls because four-way controls utilize spool valves, which have leakage that tends to allow drifting. Counterbalance valves are constructed to minimize leakage and are mounted either close to or on an associated hydraulic cylinder so that if a hydraulic line breaks, the cylinder will not collapse so as, for example, to drop a load if it is associated with a lift, boom, or manned basket. Counterbalance valves include a self-relieving feature so that excessive pressure build-up in the associated hydraulic cylinder is relieved at a set pressure, allowing a portion of the hydraulic fluid to flow from the cylinder port through the counterbalance valve to a valve port.
On machines such as slag breaking machines used in steel mills and the like, the operator has a multiplicity of switches to manipulate. At times, the operator must manipulate these switches with gloved hands. Sooner or later, the operator will inadvertently combine the wrong set of circumstances with improper switch positions and cause rapid escalation of hydraulic pressure within the cylinder. For example, the rod end of a tool cylinder in a machine, such as slag breaking machine, may be inadvertently pressurized by motion from an incompatible function, such as an improper telescoping, propelling, or hoisting function. Normally, the counterbalance valve relieves pressure to accommodate such anomalies; but, for example, if the operator inadvertently operates a retract switch for the tool cylinder while the cylinder is being mechanically pulled out by an external force, such as propelling with the tool wedged in the slag, the cylinder can rupture due to rapid pressure escalation. A double counterbalancing valve may have a poppet set to relieve at 3800 psi with a 6:1 ratio, but, because of the geometry and areas of the counterbalance valve, a 6:1 ratio valve setting can have a 7:1 multiplier effect on the relief setting. This can cause the pressure within the valve to soar to 20,000 psi. Since cylinder failure can occur at 8000-10,000 psi, expensive cylinder failures can periodically occur.